JP2010162804A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of improving image qualities (suppression of printing fluctuation, resolution) of a black dot forming section, suppressing a black nozzle from drying, and keeping a nozzle condition good. <P>SOLUTION: The image forming device has M kinds of black inks with different properties and M pieces of black heads for discharging the respective black inks and color heads for discharging the inks of other colors and forms color dots and black dots so as to satisfy the relations: M×I×A=B×C (when N≤I) and M×N×A=B×C (when N≥I), wherein the nozzle density of the black heads is N times of the nozzle density of the color heads, the interlaced number in forming the color dots in a sub scanning direction is 1/I, the pass number in forming the color dots in a main scanning direction is A, the main scanning resolution of the black dots is B times of the main scanning resolution of the color dots, the pass number in forming the black dots in the main scanning direction is C, and M, N, I, A, B, C are integers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, when a black head has a nozzle density higher than that of other color heads or a color image is formed by an apparatus having a larger number of nozzles, the number of passes in black dot formation in the main scanning direction and the main scanning of black dots The present invention relates to an image forming apparatus in which the resolution is a value different from other colors.

  The ink jet recording method is capable of high-speed recording, does not require special fixing processing when recording on plain paper, and has been attracting attention for office use because noise generation during recording is so small that it can be ignored. Yes. So far, various systems have been proposed, and various systems have already been commercialized and put into practical use. The ink jet recording method uses a recording head constituted by an ink liquid chamber and a nozzle communicating with the ink chamber. Pressure is applied to ink in the ink liquid chamber according to image information, and ink droplets are ejected from the nozzle. An image is formed by adhering to a recording material such as paper or film.

  Such an ink jet image forming apparatus discharges ink from a recording head and forms an image in a non-contact manner, so that it can record on various recording media.

  Inkjet image forming apparatuses include those in which the resolution of nozzles for ejecting black ink is higher than that for other colors, and those in which the number of nozzles for ejecting black ink is greater than for other colors. Such an inkjet image forming apparatus can perform high-resolution image formation with less head scanning for black.

  As the above-described ink jet image forming apparatus, for example, the inventions of Patent Documents 1 and 2 are disclosed. In the invention of Patent Document 1, the nozzle density of the black storage head is higher than that of the other color storage heads, and the portion formed by only the black dots in the image is formed with fewer scans and includes the color dots. In the formed part, an image is formed with a pass operation or an interlace operation. The invention of Patent Document 2 has a larger number of nozzles for black heads than the nozzles of other color heads, and the head configuration is different from that of Patent Document 1, but basically this invention also has black dots. The present invention aims to print an image with a smaller number of scans by changing the sheet feeding operation between a portion formed only with the portion and a portion including a color dot.

  However, the inkjet image forming apparatus has a problem that during the printing operation, since the recording head is on the paper surface in a decap state, the drying state of the nozzle advances, and it becomes easy to cause ejection failure due to ink thickening. The nozzle is more dry as the nozzle that discharges less ink. This is because the nozzle surface with less ejection tends to dry because the ink flow is small.

  Ink jet image forming apparatuses normally perform a maintenance operation of the nozzle surface by retracting the recording head to a maintenance area in order to maintain / recover the state of the nozzle surface. However, by performing this maintenance operation, the printing throughput is reduced, or the life of the apparatus main body is reduced because the ink is thrown away into the waste ink receiver during the maintenance.

  In the above-described inkjet image forming apparatus having a high density of black nozzles or a large number of black nozzles, the frequency of use of the black nozzles is reduced in the color printing portion, so that drying of the ink becomes more problematic. In addition, the benefits of the high-density or multi-nozzle black nozzles are limited to printing of a print area consisting only of black in the image, or monochrome printing, and so on. Cost-effective for

  Therefore, the present invention has been made in view of the above problems, and improves the image quality (printing unevenness suppression, resolution) of the black dot forming portion, suppresses drying of the black nozzle, and keeps the nozzle state good. Objective.

  In order to solve the above problems, an image forming apparatus according to the present invention includes M types of black ink having different characteristics, M number of black heads that discharge each of the black inks, a color head that discharges inks of other colors, The nozzle density of the black head is N times the nozzle density of the color head, the number of interlaces in the formation of color dots in the sub-scanning direction is 1 / I, and the number of passes for forming color dots in the main scanning direction is A, the main scanning resolution of black dots is B times the main scanning resolution of color dots, C is the number of passes for forming black dots in the main scanning direction, and M, N, I, A, B, and C are integer values. If there is, color dots and black so as to satisfy M × I × A = B × C (when N <= I) and M × N × A = B × C (when N> = I) Dots are formed.

An image forming apparatus according to the present invention includes a black head that discharges black ink and a color head that discharges ink of other colors, and the black head and the color head have the same nozzle density, and the black head The number of nozzles of the color head is L times the number of nozzles of the color head, the number of passes in forming color dots in the main scanning direction is A, the main scanning resolution of black dots is B times the main scanning resolution of color dots, and main scanning The number of passes in forming the black dot in the direction is C,
When L, A, B, and C are integer values, color dots and black dots are formed so as to satisfy L × A = B × C.

  In the image forming apparatus of the present invention, the black head has a nozzle pitch larger than a multi-color nozzle pitch, and a plurality of the black heads are arranged in a shifted manner. The nozzle density is increased.

    The image forming apparatus according to the present invention includes a monochrome / color setting unit that receives designation from the user for monochrome printing or color printing, and monochrome / color determination that determines whether the image is monochrome data or color data. And at least one of color determination means, wherein printing is performed after determining in advance whether monochrome printing or color printing is to be performed.

  The image forming apparatus according to the present invention includes at least one of an object setting unit that sets an object type according to designation from a user, an object determination unit that determines the object type, and black dots in the main scanning direction. A pass number / resolution setting unit for setting the number of passes in formation and the main scanning resolution of black dots, and the setting in the pass number / resolution setting unit is different for each type of object.

Further, the image forming apparatus according to the present invention includes an information acquisition unit that acquires at least one piece of information about the temperature and humidity of the use environment of the image forming apparatus and the printing paper,
The setting in the pass number / resolution setting means differs depending on the information acquired by the information acquisition means.

  In the image forming apparatus according to the present invention, the setting in the pass number / resolution setting unit is performed by referring to a setting table for the pass number and black dot main scanning resolution in black dot formation in the main scanning direction. It is characterized by.

  The image forming apparatus according to the present invention is configured to increase the resolution of the image data when increasing the main scanning resolution, and to form more dots than the resolution of the image data when increasing the main scanning resolution. And at least one of means for increasing the resolution by printing.

  In addition, the image forming apparatus according to the present invention can change the dot size, dot arrangement, and dot formation amount of black dots when at least one of the number of passes in black dot formation in the main scanning direction and the main scanning resolution of black dots is changed. At least one is changed.

  In the image forming apparatus according to the present invention, the dot size may be changed by changing at least one of a drive waveform and an applied voltage input to the head and a dot size to be used when a plurality of dot sizes are prepared in advance. It is characterized by being performed by changing one.

  According to the present invention, it is possible to improve the image quality (print unevenness suppression, resolution) of the black dot forming portion, suppress the drying of the black nozzle, and keep the nozzle state in a good state.

1 is a schematic configuration diagram of a mechanism diagram illustrating an example of an inkjet image recording apparatus of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a plan view of a mechanism unit and a configuration diagram of a recording head in an example of an inkjet image recording apparatus of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a control unit in an example of an inkjet image recording apparatus of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the scanning position at the time of black area printing in case the nozzle density of a black head is twice the nozzle density of a color head, and the scanning position at the time of color area printing. FIG. 5 is a diagram relating to dot formation when a color area is printed with 1-pass 1/2 interlace. It is a figure regarding the formation of the color dot and black dot at the time of printing a color area by 1 pass 1/2 interlace. It is a figure regarding formation of the color dot and black dot at the time of printing a color area by 2 pass 1/2 interlace. It is a figure which shows the number of passes of the black dot formation of the main scanning direction in the case of N = 2 and N = 4, and the main scanning resolution of a black dot. It is a figure which shows the head structure which has two types of black heads. It is a figure regarding formation of the color dot and black dot at the time of printing a color area by 1 pass non-interlace. FIG. 4 is a diagram illustrating a head configuration when the number of nozzles of a black head is three times the number of nozzles of a color head, and scan positions at the time of printing in the black region and the color region in the case of this head configuration. It is a figure regarding formation of the color dot and black dot at the time of printing a color area by 1 pass non-interlace. It is a figure regarding the table showing the setting of the pass number and main scanning resolution with respect to each object. It is a figure regarding the increase process of the main scanning resolution. It is a figure about the setting of the ink discharge amount. It is a figure about change of dot arrangement.

  Next, embodiments for carrying out the invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a mechanism unit in an example of an inkjet image forming apparatus of the present invention. As shown in FIG. 1, this inkjet image forming apparatus has an image forming unit 2 and the like inside an apparatus main body 1, and a large number of storage media (hereinafter referred to as paper) 3 are stacked on the lower side of the apparatus main body 1. A sheet feeding tray 4 that can be fed in, the sheet 3 fed from the sheet feeding tray 4 is taken in, and a required image is recorded by the image forming unit 2 while the sheet 3 is conveyed by the conveying mechanism 5. The paper 3 is discharged to the paper discharge tray 6 mounted in the above measurement method.

  In this example, the double-sided unit 7 that is detachable from the apparatus main body 1 is provided. However, in the image forming apparatus of the present invention, the double-sided unit 7 is not essential. When double-sided printing is performed when the double-sided unit 7 is provided, after one side (front side) printing is completed, the paper 3 is taken into the double-sided unit 7 while being transported in the reverse direction by the transport mechanism 5 and reversed to the other side (back side). ) Is again sent to the transport mechanism 5 as a printable surface, and the sheet 3 is discharged to the discharge tray 6 after the other side (back side) printing is completed.

  Here, the image forming apparatus 2 slidably holds the carriage 13 on the guide shafts 11 and 12, and moves the carriage 13 in a direction orthogonal to the conveyance direction of the paper 3 (main scanning) by a main scanning motor (not shown). . The paper transport direction and carriage movement are shown in FIG. In FIG. 1, a carriage 13 is equipped with a recording head 14 composed of a droplet discharge head in which nozzle holes, which are discharge ports for discharging droplets, are arranged, and an ink cartridge 15 for supplying liquid to the recording head 14. Is detachably mounted. In addition, it is also possible to adopt a configuration in which sub ink is mounted instead of the ink cartridge 15 and ink is replenished from the main ink to the sub tank.

  Here, as the storage head 14, for example, four inkjet heads that eject ink droplets of each color of black (K), cyan (C), magenta (M), and yellow (Y), or ink droplets of these colors One inkjet head having a plurality of nozzle rows that discharge the ink can be used. The number of colors and the order of arrangement are not limited to this. In the example of FIG. 2, two black heads are assembled with a half pitch shift in the nozzle row direction, and black has a head resolution twice that of the other colors.

  Further, as an ink jet head constituting the storage head 14, ink is ejected from a thermal actuator using a piezoelectric element or the like, a shape memory alloy actuator using a metal phase change due to a temperature change, an electrostatic actuator using an electrostatic force, or the like. And the like provided as an energy generating means.

  The sheets 3 in the sheet feeding tray 4 are separated one by one by a sheet feeding roller (half-moon roller) 21 and a separation pad (not shown), fed into the apparatus main body 1, and sent to the transport mechanism 5.

  Further, the transport mechanism 5 guides the fed paper 3 upward along the guide surface 23a, and also transports the paper 3 fed from the duplex unit 7 along the guide surface 23b. A transport roller 24 that transports the paper 3, a pressure roller 25 that presses the paper 3 against the transport roller 24, a guide member 26 that guides the paper 3 toward the transport roller 24, and a paper 3 that is returned during duplex printing. A guide member 27 that guides the duplex unit 7 and a pressing roller 28 that presses the paper 3 fed from the transport roller 24 are provided.

  Further, the transport mechanism 5 transports the paper 3 with the storage head 14 while maintaining the flatness of the paper 3, and charges the transport belt 33 between the drive roller 31 and the driven roller 32 and the transport belt 33. A charging roller 34, a guide roller 35 facing the charging roller 34, a guide member (plastic template) that guides the transport belt 33 at a portion facing the image forming unit 2, and a transport belt 33. It has a cleaning roller made of other porous material, which is a cleaning means for removing the adhering storage liquid (ink). A high voltage is applied to the charging roller 34 in a predetermined pattern from a high voltage circuit (high voltage power supply) (not shown).

  Here, the conveyance belt 33 is an endless belt, is stretched between the driving roller 31 and the driven roller (tension roller) 32, and circulates in the direction of arrow A (paper conveyance direction) in FIG. It is configured as follows.

  Further, on the downstream side from the transport mechanism 5, a paper discharge roller 38 for sending the paper 3 on which an image is recorded to the paper discharge tray 6 is provided.

  In the ink jet image forming apparatus configured as described above, the conveyor belt 33 circulates in the direction of the arrow A and is positively charged by coming into contact with the charging roller 34 to which a high potential applied voltage is applied. In this case, the charging roller 34 is charged at a predetermined charging pitch by switching the polarity at predetermined time intervals.

  Here, when the paper 3 is fed onto the conveying belt 33 charged at this high potential, the inside of the paper 3 is in a polarized state, and the electric charge having the opposite polarity to the electric charge on the conveying belt 33 is connected to the belt 33 of the paper 3. The charge on the belt 33 and the charge on the transported paper 3 are electrostatically attracted to each other, and the paper 3 is electrostatically attracted to the transport belt 33. . In this way, the sheet 3 strongly adsorbed to the transport belt 33 is calibrated for warpage and unevenness, and a highly flat surface is formed.

  Therefore, the recording head 14 is driven in accordance with the image signal while the sheet 3 is moved by rotating the conveyance belt 33, and the recording of the next line is performed after the sheet 3 is conveyed by a predetermined amount. When the recording end signal or the signal that the rear end of the sheet 3 reaches the storage area is received, the recording operation is ended.

  In this way, the sheet 3 on which the image is stored is discharged to the discharge tray 6 by the discharge roller 38.

  Next, an outline of a control unit in an example of the inkjet image forming apparatus according to the present invention will be described with reference to FIG. 3 which is a block diagram of the control unit.

  The control unit 100 includes a CPU 101 that controls the entire apparatus, a ROM 102 that stores programs executed by the CPU 101 and other fixed data, a RAM 103 that temporarily stores image data, and the like, while the apparatus is powered off. 1 also includes a non-volatile memory (hereinafter referred to as NVRAM) 104 for holding data, and an ASIC 105 for processing input / output signals for controlling the entire apparatus. As for the ASIC 105, a storage device classified as a high-speed device may be provided with a function for performing a part of image processing.

  The control unit 100 also includes a host I / F 106 for transmitting and receiving data and signals to and from the host side, a head drive control unit 107 and a head driver 108 for driving and controlling the storage head 14, and a main scanning motor. A main scanning motor driving unit 110 for driving 109, a sub scanning motor driving unit 112 for driving the sub scanning motor 111, an environmental sensor 113 for detecting environmental temperature and / or environmental humidity, and various sensors (not shown). I / O 114 for inputting the detection signal.

  The control unit 100 is connected to an operation panel 115 for inputting and displaying information necessary for the apparatus. Further, the control unit 100 performs on / off switching and output polarity switching control of the high voltage circuit (high voltage power source) 116 that applies a high voltage to the charging roller 34.

  Here, the control unit 100 receives print data including image data from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera. The data is received by the host I / F 106 via the network.

  Then, the CPU 101 reads and analyzes the print data in the reception buffer included in the host I / F 106, performs data rearrangement processing and the like (in some cases, part of image processing) by the ASIC 105, and the head drive control unit 107. Transfer image data to. The conversion of print data for image output into bitmap data may be performed by storing font data in the ROM 103, for example, or image data is expanded into bitmap data by a host-side printer driver. You may make it transfer to this apparatus.

  When the head drive control unit 107 receives image data (dot pattern) corresponding to one row of the storage head 14, the dot pattern data for one row is serially transmitted to the head driver 108 in synchronization with the clock signal. The latch signal is sent to the head driver 108 at a predetermined timing.

  The head drive control unit 107 includes a ROM (which can also be configured by the ROM 102) storing pattern data of a drive waveform (drive signal), and a D / A for D / A converting the drive waveform data read from the ROM. A drive waveform generation circuit including a waveform generation circuit including a converter and an amplifier is included.

  The head driver 108 also includes a shift register that receives a clock signal from the head drive control unit 107 and serial data that is image data, and a latch circuit that latches a register value of the shift register using a latch signal from the head drive control unit 107. A level conversion circuit (level shifter) that changes the output value of the latch circuit, an analog switch array (switch means) that is controlled to be turned on / off by the level shifter, and the like, and controls on / off of the analog switch array. In this way, a required drive waveform included in the drive waveform is selectively applied to the actuator means of the recording head 14 to drive the head.

  As an embodiment of the present invention, an inkjet image forming apparatus having a KCMY four-color configuration in which the nozzles of the K (black) head have twice the density of the nozzles of the CMY head will be described. In such an apparatus, the nozzle density of the black head is made higher than the nozzle density of the color head, the paper conveyance amount is changed between the black area and the color area of the image, and the paper conveyance is performed between monochrome printing and color printing. There are technologies that increase the printing speed by changing the amount.

  For example, as shown in FIG. 4A, when monochrome printing or when forming a black region in an image, an image is printed with a small number of scans using only a high-resolution black head to form a color region. In this case, as shown in FIG. 4B, an interlace or a pass is inserted to form an image. As a result, the number of scans in the black image area is reduced, and the printing speed can be increased.

  However, when forming a color area, the black head is also pulled by the color head and must be scanned. For example, assuming that the resolution of the black nozzle in FIG. 4 is 600 dpi and the resolution of the color nozzle is 300 dpi, when forming a 600 dpi color image in the sub-scanning direction, the black nozzle can complete image formation in one scan. Nevertheless, since the color nozzle needs two or more scans, the black nozzle has to be two or more scans.

  In such a case, there are cases where the black head uses only nozzles in the same arrangement as the nozzles of the color head, and there are cases where ink is not ejected in one of the two scans. However, in any case, the dry state of the nozzles that are not used advances, and discharge defects are likely to occur. In particular, in the former, a specific nozzle is left in a decap state until image formation is completed, and there is a risk of nozzle drying. In the latter case, the drying of a specific nozzle does not proceed extremely, but the risk of nozzle drying increases because one of the two scans continues to be decapped. Also, the larger the paper size, the longer it takes to scan, and the drying problem becomes more serious.

  Also, a black head having a high-resolution nozzle arrangement is not effectively used in the color area. In order to realize a high-resolution head, it is necessary to increase the nozzle pitch or dispose the nozzles and arrange a plurality of heads. In both cases, the technical and cost burdens are large, and the cost performance of the device is deteriorated.

  The present invention relates to the use of the black nozzle when printing the color area, and by increasing the number of passes in the main scanning direction or the main scanning resolution, the dots ejected by the black nozzle when scanning the color area. It improves image quality and prevents nozzle drying.

  As an example, a case will be described in which a 600 dpi × 600 dpi color image is formed by a one-pass 1/2 interlace operation when the nozzle density of the black head is 600 dpi and the nozzle density of the color head is 300 dpi. Here, the dot formation interval in the main scanning direction that can be ejected by the nozzles of each head is 600 dpi per scan.

  As shown in FIG. 5, since the color nozzle has a density of 300 dpi, it is necessary to perform an interlace operation in order to set the sub-scanning resolution to 600 dpi. When dots in the main scanning direction are completed in one scan (so-called one-pass printing), a two-scan operation is performed to form a color image of 600 dpi × 600 dpi, so the density is increased during the conventional printing operation described above. In addition, the black head cannot be effectively used, and the black nozzle may be dried. If the present invention is applied, the black head also performs the operation for two scans. However, as shown in FIG. 6, the main scanning resolution is doubled or the number of passes for forming the main scanning direction dots is two. Thus, the black head can be used effectively and the drying problem of the black nozzle can be solved.

  FIG. 6 shows dot formation when the number of passes and the main scanning resolution are changed. FIG. 6A shows color dot formation, in which 1 dot is printed on the first scan and 2 dots are printed on the second scan.

  When the number of passes for forming black dots in the main scanning direction is two, dots in the main scanning direction are divided into two scans (FIG. 6B). Thereby, since all the black nozzles are used once during one scan, the drying problem of the black nozzles is solved. In FIG. 6B, dots 1 and 2 are printed on the first scan, and dots 3 and 4 are printed on the second scan.

  When the main scanning resolution is doubled, the dot ejection timing may be shifted by half a pitch in the first and second scans (FIG. 6C). In this way, even if dots can be formed only at an interval of 600 dpi per scan, dots can be formed at a double 1200 dpi pitch by performing two scans. In FIG. 6C, dots 1 and 2 are printed in the first scan, and dots 3 and 4 are printed in the second scan.

  In general, ink is ejected by reading an encoder sheet placed in the head movement direction and detecting the position in the main scanning direction. The reading resolution of this encoder is equal to or higher than the recording resolution. Alternatively, the ink may be lower than the recording resolution, and the ink ejection timing may be realized by software, even at the ink ejection timing.

  Further, by making the number of passes two, the drying problem is solved and the occurrence of streaks at the black dot forming portion and printing unevenness can be prevented.

  Inkjet image forming method applies pressure to ink and ejects ink from nozzles to form dots, but as the recording frequency increases, it becomes difficult to control the meniscus of the ink level, and the target ink droplet volume can be ejected. In some cases, the dot ejection accuracy may deteriorate. In addition, there may be a problem of nozzle omission or bending due to nozzle manufacturing variations or dry conditions. At this time, the ink may not be ejected well or the dots may deviate from the target coordinates, and these ink ejection failure problems may lead to streaks, printing unevenness, and graininess on the image. .

  Multi-pass printing is known as a technique for reducing these. In multi-pass printing, dots in the main scanning direction are formed a plurality of times using different nozzles, thereby making it possible to make the influence of missing or bent inconspicuous. Further, since the dots in the main scanning direction are divided and formed by a plurality of scans, the recording frequency is suppressed and the ink ejection stability is improved. Depending on the recording paper, ink may bleed or not easily dry, which may cause image quality to deteriorate, but increasing the number of passes can ensure the ink drying time and prevent these phenomena. It can also be suppressed.

  As described above, according to the present invention, it is possible to benefit from at least one of the improvement in the main scanning resolution of black dots and the improvement in image quality due to the multi-pass formation. Further, when the color region is printed, the decap time of the black nozzle is reduced, and the specific nozzle is not left unused, so that the nozzle drying problem is less likely to occur.

  In the above example, the case where the color area is printed with 1 pass and 1/2 interlace has been described. However, even when the color area is formed with 2 passes, the number of black dot passes and the main scanning resolution are set as shown in FIG. Can be changed. In FIG. 7, the number assigned to a dot indicates how many scans the dot is shot.

  From the above, when the nozzle density of the black head is N times the nozzle density of the color head, the number of interlaces in the color dot formation in the sub-scanning direction is 1 / I, and the number of passes of color dot formation in the main scanning direction is A And the black dot main scanning resolution is B times the color dot main scanning resolution, and the number of black dot formation passes in the main scanning direction is C.

I × A = B × C (when N <= I),

N × A = B × C (when N> = I),

It can be seen that the number of black dot passes and the main scanning resolution can be set within the range. Here, N, I, A, B, and C are integers. FIG. 6 shows a case where N = 2, and FIG. 7 shows a case where N = 4. FIG. 8 shows the number of black dot passes and the main scanning resolution possible when N = 2 and N = 4.

  As a method of increasing the density of the black nozzles, a black head having a nozzle density higher than that of the color nozzles may be used, or the nozzles of a plurality of black heads may be shifted as shown in FIG. You may implement | achieve by arrange | positioning. In the latter case, since the same device can be used for all the heads of the same K (black) CMY, there is a great merit in terms of cost. Further, the arrangement of the nozzles including the color order is not particularly limited. The same applies to the following embodiments.

  Next, as another embodiment, an example of a nozzle configuration as shown in FIG. 9 will be described. In the previous embodiment, the density of black nozzles is higher than that of other color nozzles, but in this example, there are more black nozzle arrays than other colors. This nozzle row is called K1 and K2, respectively.

  With such a configuration, there is an inkjet image forming apparatus that ejects different sizes of ink from K1 and K2 or ejects different types of ink. For example, K1 is in charge of forming large dots, K2 is in charge of forming dots smaller than K1, and forms images, K1 is an example of ejecting pigment ink, K2 is an example of ejecting dye ink, and K1 is a high density There is an example in which black ink is ejected and K2 is ejected with a lower density than K1.

  The former includes, for example, K1 nozzles used for low-resolution images to fill the paper with large dots, and high-resolution images intended to improve printing speed by filling the paper using K2 nozzles, or both nozzles. Is used to increase the size of dots that can be handled to improve gradation and graininess. For the latter, pigment ink with low bleeding and strong dye ink and dye ink with good color development are used depending on the image to be printed and the paper to be used. There are things aimed at improving sex.

  In any case, even in such a nozzle configuration, the number of nozzles that must be maintained is large, and the drying problem in the nozzle state is the same as in the previous embodiment. Therefore, even in such a case, it is possible to improve the image quality while maintaining the nozzle state by increasing the number of black passes and the main scanning resolution.

  For example, as shown in FIG. 10, black dots in the main scanning direction are divided and formed by the K1 nozzle and the K2 nozzle, and the number of passes is increased, and the discharge timing of the K1 ink and the K2 ink is shifted to thereby change the main scanning resolution. It becomes possible to improve.

  In this configuration, the number of passes and the main scanning resolution can be improved even when color printing is performed with one pass non-interlace. For example, if the number of black nozzles is double that of color, when the color is one-pass non-interlace, it is possible to pass the number of passes twice or double the main scanning resolution only for black. .

  When the number of black nozzles is M, the number of black nozzles is M times the number of nozzles of other colors. Here, M is an integer. When forming a color image, assuming that the number of passes for forming a color dot is A, the main scanning resolution for black dots is B times the main scanning resolution for color dots, and the number of passes for forming black dots in the main scanning direction is C. , It is possible to set the number of black dot passes and the main scanning resolution within the range where M × A = B × C. Here, A, B, and C are integers. FIG. 10 shows dot formation when the sub-scanning direction resolution of the black head and the color head is 300 dpi, and M = 2. In FIG. 10, the numbers assigned to the dots indicate the scan number at which the dots are shot.

  As another embodiment, a head configuration as shown in FIG. 11 is also conceivable. When using such a head to print monochrome or black areas, there are some that carry paper at a higher speed than when printing color images or color areas, and in this case color printing is also possible. Sometimes, the black (K) head needs to perform the same scanning operation as CMY, and the nozzles cannot be used effectively.

  For example, when a color area is printed with a head as shown in FIG. 11, to complete the color (CMY) area, the head needs to be scanned at least three times. Since image formation can be completed once for black, the number of passes is increased and the main scanning resolution is improved by using these three scans. In the case of forming a color area by one-pass non-interlace as shown in FIG. 12, for example, black nozzles have three times the chance of forming dots at the same sub-scanning position, so the number of passes is tripled. Alternatively, the main scanning resolution can be tripled. Also in this example, it is possible to increase the number of passes and improve the main scanning resolution in both cases where interlace is included and not included. When the number of black nozzles is L times the number of other color nozzles, when forming a color image, the number of passes for forming a color dot is A, and the main scanning resolution for black dots is B, which is the main scanning resolution for color dots. When the number of passes for black dot formation is C and the number of passes for black dots is C, the number of passes for black dots and the main scanning resolution can be set within a range where L × A = B × C. Here, L, A, B, and C are integers. FIG. 12 is a diagram showing black dot formation when L = 3. In FIG. 12, the numbers assigned to the dots indicate at what scan the dots are shot.

  In addition, since the increase in the number of passes and the improvement in the main scanning resolution described above function when performing color printing, it is preferable to determine whether to perform color printing. For example, whether the user sets himself / herself for monochrome printing or color printing, or automatically searches whether there is a color element in the image data to be printed, and the number of passes above when performing color printing Increase the main scanning resolution. Also, when performing color printing, since there are portions where there is no color area, it is preferable to increase the number of passes and improve the main scanning resolution for the portion where there is a color area. .

  The increase in the number of passes and the improvement in the main scanning resolution are preferably set according to the objects (characters, lines, photographs, images) in the image. For example, the outline shape is important for characters, lines, etc., so the resolution should be increased, and images, photographs, etc. must be free of uneven printing and have good gradation and graininess. It is preferable to increase the number.

  It is also preferable to set the number of passes and the main scanning resolution according to the print mode, print environment, and paper to be used. For example, the importance of the number of passes and the main scanning resolution differs depending on whether the original color area is printed in one pass or multi-pass. In the case of one-pass printing, if a nozzle is defective, the influence of the nozzle defect appears as a straight stripe in the image, so it is preferable to increase the number of passes rather than to improve the resolution. In addition, the image quality improvement due to the improvement in resolution is conspicuous until the main scanning resolution is, for example, near 1200 dpi, but if it exceeds that, the image quality cannot be significantly improved. Therefore, when a sufficient resolution can be expected, it is more effective to allocate the subsequent scans to increase the number of passes to reduce the printing unevenness and the load on the recording head.

  Also, the ink ejection characteristics differ in the printing environment, and the nozzles are likely to dry depending on the temperature and humidity. Further, since ink ejection may become unstable, it is preferable to actively increase the number of passes in such an environment to prevent image deterioration. Regarding the paper, even if the same amount of ink is ejected on different papers, the ease of ink bleeding and thirst on the paper will differ, and the characteristics of the printed image will also differ. Therefore, for example, it is preferable to preferentially increase the number of passes on a paper with a large ink bleeding or a paper that dries slowly.

  In this case, the setting of the number of passes and the resolution may be provided in a table format as in the example of FIG. In the example of FIG. 13, an object that emphasizes the outline shape of characters and lines has a relatively high resolution, and an object that emphasizes printing unevenness (such as uneven stripes and drying unevenness), dryness, and graininess, such as a photograph or an image, The number of passes is set relatively high. The reason why the number of passes is set to be relatively high in an object where graininess is important is that the dot shape is stable.

  Further, it is preferable to change the number of black passes and the resolution in accordance with the environment and the characteristics of the ink and the head. For example, in an L / L environment where the temperature and humidity are lower than predetermined values, there is a high possibility that white streaks will appear and information will be lost if there are omissions, so the number of passes is also increased for characters and lines. In an H / H environment where the temperature and humidity are higher than the predetermined values, the graininess is predicted to deteriorate when the ink dot shape varies, so photographs and image objects that are easily affected by the graininess. For example, the number of passes is increased. In addition, in the environment setting, for example, a preset temperature value and humidity value are stored in the apparatus as threshold data, and compared with a temperature / humidity value (actual value) acquired by a sensor in the apparatus. You may make it determine the environment to perform.

  Although not described in detail in FIG. 13, the number of passes is also set for the paper in accordance with dot spread and drying characteristics. For example, it is preferable to set the resolution to be higher for a paper in which the shape of the dot is easily visible and the edge contrast is conspicuous, and to increase the number of passes for the paper having poor drying property so as to have a drying time.

  Further, regarding the processing in the case of increasing the main scanning resolution, data may be expanded as the increased resolution as shown in FIG. 14A, or the main scanning doubled amount as shown in FIG. 14B. The main scanning resolution may be increased by continuing the data in the main direction.

  Further, when the main scanning resolution is increased, the method of filling the paper is different from that before the increase. If the dot diameter is kept at a low resolution, the spread of the dots is large, and the amount of ink adhering to the paper surface increases, so the benefits of improving the resolution may not be achieved. Therefore, it is more preferable to change the dot diameter to be used in accordance with the change in resolution. As a method of changing the dot diameter, a method of changing the drive waveform input to the head may be used, or the ink discharge amount may be adjusted and controlled by changing the voltage value based on the same waveform. In addition, in an apparatus capable of ejecting dots of a plurality of sizes, for example, large, medium, and small sizes, for example, all of large, medium, and small are used for low resolution, and medium and small for high resolution. The size may be changed by using only a small size. Further, instead of the dot size, a method of changing the ink adhesion amount may be used or used together. When the resolution increases, the amount of ink attached increases in order to form a high-density dot, so the amount of ink attached is changed to a value suitable for the resolution. A halftone parameter that matches the resolution may be prepared and processed, or the input value may be multiplied by a coefficient, or may be corrected by a table as shown in FIG.

  As for the number of passes, only the way of hitting is changed and the position and number of formation are not changed. However, since the dots are divided and formed, the ink drying time can be secured and the ink is resistant to bleeding and beading. Therefore, it is possible to increase the ink adhesion amount and to output a higher density. Also for this, a dedicated parameter may be provided, a coefficient may be applied to the input value, or correction may be performed using a table. Further, when the multipass is performed, as shown in FIG. 16B, dots formed at the same place a plurality of times may be created to increase the adhesion amount. Normally, dots are formed alternately as shown in FIG. 16 (a). However, as the number of passes increases, the resistance to bleeding and the dryness are improved. It becomes possible to provide an image.

  In particular, such a technique is effective because the ink adhesion amount cannot be increased only by correcting the input value for the solid portion. In addition, when the present invention is applied using black inks having different densities in the above-described embodiments, even if the resolution and the number of passes are increased on the dot formation, There may be a case where the image density does not increase. Even in such a case, the usage ratio of inks with different densities may be set so that more dots are formed with dark ink, or a place where dots are formed with both dark and light inks may be created. preferable. These processes may also have a special halftone parameter, or a dot patterning method, or a pattern to be overlaid, and a corresponding pattern is made by a plurality of scans (or heads). This can be done by repeating the process.

  Note that the dot formation order when the number of passes and the resolution described above are changed is not limited to the order described in the drawing, and dots may be formed in a specific strike order pattern, and there are several types. The pattern may be combined to fill the page.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments thereof, various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the invention as defined in the claims. is there.

DESCRIPTION OF SYMBOLS 1 Inkjet image forming apparatus 2 Image forming part 3 Paper 5 Conveying mechanism part 7 Duplex unit 14 Recording head 33 Conveying belt

JP 09-290519 A JP 2005-335192 A

Claims (10)

M kinds of black inks having different characteristics and M black heads for ejecting each of the black inks;
A color head for discharging ink of other colors,
The nozzle density of the black head is N times the nozzle density of the color head;
The number of interlaces in the color dot formation in the sub-scanning direction is 1 / I,
The number of passes for forming color dots in the main scanning direction is A,
The main scanning resolution of black dots is B times the main scanning resolution of color dots,
Let C be the number of passes for black dot formation in the main scanning direction.
When M, N, I, A, B, and C are integer values,
M × I × A = B × C (when N <= I),
M × N × A = B × C (when N> = I),
An image forming apparatus which forms color dots and black dots so as to satisfy It has a black head that ejects black ink and a color head that ejects ink of other colors,
The black head and the color head have the same nozzle density,
The number of nozzles of the black head is L times the number of nozzles of the color head;
A is the number of passes in forming color dots in the main scanning direction.
The main scanning resolution of black dots is B times the main scanning resolution of color dots,
Let C be the number of passes in black dot formation in the main scanning direction.
When L, A, B, and C are integer values,
An image forming apparatus, wherein color dots and black dots are formed so as to satisfy L × A = B × C.   The nozzle density of the black head is increased by at least one of making the nozzle pitch of the black head larger than the multi-color nozzle pitch and displacing the plurality of black heads. The image forming apparatus according to claim 1. Monochrome / color setting means that receives designation from the user as to whether to perform monochrome printing or color printing;
At least one of monochrome / color determination means for determining whether the image is monochrome data or color data;
The image forming apparatus according to claim 1, wherein printing is performed after determining in advance whether monochrome printing or color printing is to be performed. An object setting means for setting an object type according to a specification from the user;
At least one of object discriminating means for discriminating the type of the object;
A pass number / resolution setting means for setting the number of passes in black dot formation in the main scanning direction and the main scanning resolution of the black dots,
5. The image forming apparatus according to claim 1, wherein the setting in the pass number / resolution setting unit is different for each type of the object. 6. Having an information acquisition means for acquiring temperature and humidity of the environment in which the image forming apparatus is used and at least one piece of information about the printing paper;
The image forming apparatus according to claim 1, wherein the setting in the pass number / resolution setting unit is different depending on the information acquired by the information acquisition unit.   7. The setting in the pass number / resolution setting means is performed by referring to a setting table for the number of passes in black dot formation in the main scanning direction and the main scanning resolution of black dots. The image forming apparatus according to claim 1. Means for increasing the resolution of the image data when increasing the main scanning resolution;
8. The apparatus according to claim 1, further comprising means for increasing the resolution by printing so that more dots are formed than the resolution of the image data when the main scanning resolution is increased. The image forming apparatus according to claim 1.   When at least one of the number of passes in black dot formation in the main scanning direction and the main scanning resolution of black dots is changed, at least one of the dot size, dot arrangement, and dot formation amount of the black dots is changed. The image forming apparatus according to claim 1.   The dot size is changed by changing at least one of the drive waveform and applied voltage input to the head and the dot size used when a plurality of dot sizes are prepared in advance. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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